Replace resource bits-service-system-test-source with git-bits-service-release
Replace resource bits-service-system-test-source with git-bits-service-release

This had impractical side effects: the original resource would take the commit from the  folder and then try to clone submodules with specific shas. Those submodule shas were sometimes not available because  folder sha was too old.

cloudfoundry-incubator/bits-service-ci,cloudfoundry-incubator/bits-service-ci,cloudfoundry-incubator/bits-service-ci